A respirator filter of this type has become known from German Patent No. DE-PS 11,23,918. The prior-art respirator filter has a pot-shaped filter housing with a flange acting as a contact surface for a filter element, which is pressed against the flange by means of a housing cover closing the filter housing. The filter housing is perforated in the middle, and it has a cylindrical flow channel there, which passes through the filter element or the filter elements. The flow channel has a sealing surface as the contact surface for the filter element, and the filter element is fixed by the housing cover on both the flange and the sealing surface at the same time. To seal the filter element against the housing or to seal individual filter elements arranged in parallel to one another, sealing rings are provided. The sealing rings are compressed when placed on the housing cover, and they press the filter element against the flange and the sealing surface due to their elastic deformation.
To uniformly distribute the air to be purified over the filter surface, a free space in the form of a spacer section is provided between the filter element and the housing cover. With the free space an air distribution chamber is formed, provided between the filter element and the housing cover.
One disadvantage of the prior-art respirator filter is that its manufacture is complicated, because filter elements and sealing rings must be placed into the filter housing in a defined sequence, and a great number of individual parts are needed to assemble the filter.
German Patent No. DE-PS 655,223 discloses a respirator filter with a pot-shaped filter housing and with a filter element placed into the filter housing, in which the filter element is in contact with a flange folded outwards on the filter housing, and it is pressed against the flange with a housing cover. The housing cover is firmly connected to the filter housing by rolling its outer edge onto the flange.
The disadvantage of this prior-art respirator filter is that only the size of the flat surface of the flange is decisive for achieving good sealing between the filter housing and the filter element. Since such respirator filters can also be inserted into filter mounts, this predetermines defined assembly dimensions, so that the flange surface usually must be limited to the absolutely necessary dimension, which may lead to problems in terms of sealing in some cases.
British Patent No. GB-PS 438,556 discloses a respirator filter with a pot-shaped filter housing, in which the filter element is placed over the flanged edge of the filter housing and is rolled onto the edge together with the housing cover.
Even though the prior-art respirator filter has more favorable assembly dimensions than an outwardly projecting flange, the sealing of the filter element against the filter housing is not satisfactory.
West German Patent No. DE-PS 702,119 discloses a respirator filter, in which the filter element is accommodated in a holder on the housing cover of the filter housing, and the housing cover is connected to the filter housing in the manner of a double fold. Even though a good gas-tight connection of the housing cover to the filter housing is ensured in this prior-art respirator filter, and this connection can also easily be bent up again with special machines, a separate holder is necessary for fastening the filter element.